Dispersible granular substrate for pesticide delivery

ABSTRACT

An inert dispersible granular substrate is suitable for use as a carrier for chemical agents. The granular substrate is comprised of one or more mineral components, the one or more mineral components having a bulk density of greater than about 70 pounds per cubic foot, one or more dispersibility additives; and one or more water soluble binders. The granular substrate has a bulk density of from greater than 55 pounds pcf to about 70 pcf, a water dispersibility of less than 5 minutes, a pH of from 6 to 8, and sufficient strength to survive formulation processing after 3 days of continuous exposure to a temperature of approximately 75° F. and a relative humidity of approximately 95%. Preferably, an active pesticide is applied to the dispersible granular substrate. The water dispersible granular substrates may be produced by forming a granular substrate admixture, pelletizing the admixture to form granular substrates, and drying the granular substrates.

RELATED APPLICATION

This application is claiming the benefit, under 35 U.S.C. § 119(e), ofthe provisional application filed Oct. 11, 2005 under 35 U.S.C. §111(b), which was granted serial number 60/725,266. This provisionalapplication is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to a dispersible granular substrate suitable foruse as a carrier for chemical agents, as well as a method for producinga granular substrate. More particularly, this invention relates to amedium weight dispersible granular substrate.

Generally, granular substrates are utilized as carriers for activechemical agents, such as for example herbicides or other pesticides. Theterms “pesticide” or “pesticides” are used herein in the broad sensethat includes herbicides. The carriers, with the active chemical agents,are utilized to distribute the active agent over a broad area. Thecarriers are generally inert compounds that, upon application, breakdown over time.

Existing water soluble granular substrates are nutrient-based carriers,conventionally formed of ammonium sulfate. However, ammonium sulfateacts as a fertilizer, providing a growth response that may not bedesired, and can burn turf if misapplied or applied at high rates as,for example, a mound treatment for ant control.

In addition, conventional granular substrates often have a tendency tobreak apart, thus creating handling and distribution problems. Granularsubstrates that resist attrition are preferred because they will notdegrade and therefore maintain their particle size during handling.While resistance to attrition is important, in some applications it ispreferable that the carrier compound breakdown or disintegrate uponexposure to water.

SUMMARY OF THE INVENTION

The invention is a dispersible granular substrate suitable for use as acarrier for chemical agents. The granular substrate is comprised of oneor more mineral components, the one or more mineral components having abulk density of greater than about 70 pounds per cubic foot, one or moredispersibility additives; and one or more water soluble binders. Thegranular substrate has a bulk density of from greater than 55 pounds pcfto about 70 pcf, a water dispersibility of less than 5 minutes, a pH offrom 6 to 8, and sufficient strength to survive formulation processingafter 3 days of continuous exposure to a temperature of approximately75° F. and a relative humidity of approximately 95%. Preferably, anactive pesticide is applied to the dispersible granular substrate.

According to another aspect of the invention, water dispersible granularsubstrates may be produced by forming a granular substrate admixture bymixing one or more mineral components, the one or more mineralcomponents having a bulk density greater than about 70 pounds pcf, oneor more dispersibility additives, and one or more water soluble binders.The admixture is then pelletized to form granular substrates. Thegranular substrates are dried at a temperature sufficient to removeexcess moisture and produce finished granular substrates that have abulk density of from greater than 55 pounds pcf to about 70 pcf and awater dispersibility of less than 5 minutes.

DESCRIPTION OF THE INVENTION

In accordance with the present invention, there is provided adispersible granular substrate composition that is suitable for use as acarrier for active chemical agents. The present invention also includesa method for forming the dispersible granular substrate.

The dispersible granular substrate of the invention closely matches thedensity and “spreadability” of ammonium sulfate, but is “inert” in thesense that it does not contain a significant amount of plant nutrientsand thus does not provide a growth response, is less hygroscopic, is notphytotoxic, and exhibits good chemical and physical stability. Thedispersible granular substrate preferably has a pH of from 6 to 8, mostpreferably from 6.5 to 7.5, to provide a substrate with minimalreactivity.

Further, the dispersible granular substrate of the invention does notdegrade during handling but preferably breaks down when exposed tomoisture or water. The resistance to attrition ensures the properdistribution of the active chemical agent upon application. The abilityto disintegrate upon exposure to water is preferred to provide theactive chemical agent to the soil.

The dispersible granular substrate composition of the present inventionincludes one or more mineral components, one or more dispersibilityadditives, and one or more water soluble binders. The mineral componentin the granular substrate is preferably one or more selected from thegroup consisting of dolomite and limestone. The mineral components makeup about 65 wt % or more of the dispersible granular substrate. Ingeneral, the mineral components have a sizing of 100% passing through a30 mesh screen and 50% or more passing through a 200 mesh screen. Themineral components have a preferred sizing of about 100% through a 50mesh screen and 80% or more through a 200 mesh screen. The noted meshsizes and all those mentioned hereafter conform with U.S. standard sievesizes. Additionally, the mineral components have a bulk density ofgreater than about 70 pounds per cubic foot, and preferably have a bulkdensity of about 75 to about 90 pounds per cubic foot. The sizing of themineral components may vary with respect to other ingredients utilizedin the agglomerated substrate. In addition to the preferred mineralcomponents, other stone or mineral dust compounds conforming with thesize and bulk density parameters may be suitable for use with thepresent invention.

One or more dispersibility additives are utilized with the presentinventive composition. The granular substrates of the invention includeabout 0.5 wt % to about 25 wt % of such additives, preferably from about1 to 2 wt %. The dispersibility additives are generally inert compoundspreferably having, in the case of solid dispersibility additives, asizing of at least 20% passing through a 40 mesh screen. It is preferredthat any solid dispersibility additives have a sizing of 100% passingthrough a 40 mesh screen. Additionally, the dispersibility additive(s)should be a non-fibrous material as indicated by the sizing parameters.Fibrous material can adversely impact the dispersibility and the flowcharacteristics of the finished granular substrate. The dispersibilityadditives are preferably one or more selected from the group consistingof expanded silica, fly ash, hydrated lime, wood flour, wood particleboard flour, distiller's dried grain, thin stillage, ground wheat straw,cellulose, glycerins, glycols, cellulose, clay, soy flour, and mineraloil. However, other inert compounds providing the desired dispersibilityand flow characteristics to the finished granular substrate may besuitable for use in the present inventive composition.

A preferred embodiment includes the use of wood flour resulting fromfinely milled wood particle board. The wood particle board typicallycontains approximately 10 wt % of a urea-formaldehyde resin. Anotherpreferred embodiment includes the use of wheat straw flour resultingfrom finely milled wheat straw particle board. The wheat straw particleboard contains a diphenylmethane diisocyanate resin. In both cases, theadditional resin may assist in producing a granular substrate that doesnot degrade during handling but breaks down upon exposure to water.

A binder is utilized to agglomerate the ingredients of the presentinvention. In these embodiments, the binder is utilized at an amount upto about 20 wt % (dry basis) of the granular composition. The preferredamount of binder is generally 2 wt % to 20 wt %. The binder utilizedwill bind the ingredients into granular substrates which resistattrition, will not degrade and therefore maintain their particle sizeduring handling. The binder is such that the resulting granularsubstrate has a resistance to attrition (RTA) value, in accordance withASTM E 728-91 Volume 11.04, of at least 85%, preferably at least 90%. Inaddition, the selected binder needs to be sufficiently water solublethat the resulting granular substrate disperses quickly in water.

The binder is preferably selected from the group consisting of brewerscondensed solubles, fermentation solubles, lignosulfonate, sodiumcarbonate lignin, cane molasses, beet syrup, beet molasses, desugaredbeet molasses, whey, starch, soy solubles with cane molasses or thelike, hydrolyzed collagen, amino acid solutions, citrus residium,cellulose derivatives, hemicellulose extract (such as the Temulosehemicellulose extract from Temple-inland Forest Products Division ofDibold, Texas), urea liquor, or cellulose based polymer binders. Thepreferred binder is calcium lignosulfonate, such as the calciumlignosulfonates available from Flambeau River Papers, Inc. of ParkFalls, Wis. Most preferred is the Ca Lignin available from FlambeauRiver Papers, Inc. that has been desugared.

Other water soluble binders having equivalent properties to, forexample, the brewers condensed solubles, may be suitable for use in thepresent inventive composition, although economics may mitigate againsttheir use.

The binder is generally added to the composition as a solution. Thesolution is typically provided as a water based slurry having about 40%to 50% solids by weight and weighing about 10 pounds per gallon. Thebinder may also be added as a powder and mixed with the other dryingredients, subsequently mixing in an amount of water.

The composition of the present invention is generally produced by firstcreating an admixture of the noted components within the specifiedranges. The mixing of the components may occur in either a batch orcontinuous mixing process. Conventional mixing devices are suitable foruse with the present invention. The components should be thoroughlymixed at conditions which prevent degradation or compaction of thematerials. During the mixing step, the binder composition is generallyadded to the mixture as a solution. Optionally, at least part of thewater soluble binder may be added to the pelletizing apparatus duringpelletizing. Additional water, up to about 15% by weight, may benecessary for agglomeration of the materials in the inventivecomposition.

The admixture is then fed into a pelletizing apparatus to produce thedispersible granular substrate of the present invention. Conventionalpelletizing equipment is suitable for use in producing the substrate inpellet form. The preferred pelletizing equipment is a pelletizing pan.Additionally, drum granulators or other types of granulation equipmentmay be used to produce the granular substrate of the present invention.

Water may be added to the mixture during the pelletizing step of theprocess to assist in granulation of the material. The water is generallyadded at an amount which results in no greater than 35% by weight in thesubstrate.

In accordance with the present invention, the operation of a pelletizingpan may vary with the specific formulation or ingredients in order toproduce a granular substrate with the preferred properties. For example,feed rates and locations of the admixture or the water, the angle of thepan, the speed of rotation of the disc, or the depth of the pan may bevaried to produce the desired product. One skilled in the art ofpelletizing is capable of recognizing the variables and makingadjustments to obtain the granular substrate in pellet form.

The dispersible granular substrate may then be dried to a temperature ofabout 240° F. to about 300° F. to remove excess water utilized duringthe agglomeration of the components. The pellet is preferably dried to atotal moisture content of 8% or less in accordance with ASTM standard D5033 Volume 11.04. The substrates have a preferred total moisturecontent of 2.0% or less, more preferably 1.25% or less. The uppertemperature limitation during the drying step prevents the degradationor burning of the organic binder in the granular substrate. Thesubstrates may be dried in conventional drying units, such as forexample a fluid bed dryer or a rotary dryer.

The resulting granular substrates are then screened to remove oversizedand undersized granular substrates. The improperly sized material may berecycled to the mixing stage or milled to the appropriate size andrescreened.

The dispersible granular substrates of the invention have a bulkdensity, as measured by ASTM E 727 Volume 11.04 standards, of fromgreater than 55 pounds per cubic foot (“pcf”) to about 70 pcf,preferably from about 57 pcf to about 67 pcf, more preferably from about59 pcf to about 65 pcf, and most preferably about 62 pcf.

The size of particles is determined by the size guide number/uniformityindex system used in the fertilizer industry. The substrates of thepresent invention have a size guide number between 50 and 300,preferably between about 100 to about 230, and preferably have auniformity index of at least 35, more preferably at least 40. The sizeguide number describes the relative particle size and is obtained bymultiplying the average particle size, in millimeters, by 100. Theuniformity index is a comparison of large particles to small particles.The index is expressed as a whole number between 1 and 100 with highernumbers indicating better uniformity and tighter size range.Additionally, the sizing may be determined in accordance with ASTM E728-91 Volume 11.04 wherein the sizing is preferably 20% or more passingthrough a 14 mesh screen and retained on a 40 mesh screen.

The dispersible granular substrate should be strong enough so that theparticle does not significantly degrade during normal conveying andhandling operations. The degradation of granular substrates would resultin an increase in fine material which in turn would increase the bulkdensity. Additionally, dust or powder material absorbs more chemicalagent and therefore would result in the improper distribution of theactive chemical agent upon application.

It is preferred that the granular substrate not degrade until exposed towater. However, it is also important that the substrate notsignificantly degrade with high humidity. The ability of the granularsubstrate of the present invention to degrade with water is generallymeasured by means of a water dispersibility test. The test involvesplacing about 10 grams of the granular substrate into 100 ml of water atroom temperature in a closed glass container. The container is theninverted and the time is observed until the material completelydisperses. After every minute, the container is inverted. The granularsubstrate of the present invention has a dispersibility time ofgenerally less than 5 minutes, preferably less than 3 minutes, and mostpreferably less than 1 minute.

It is further preferred that the granules of the invention exhibitbetter storability than conventional pelleted lime. In this regard, itis more specifically preferred that the granules maintain sufficientstrength to survive formulation processing after at least 3 days, andmore preferably 4 days for use in tropical climates, of continuousexposure to a temperature of approximately 75° F. and a relativehumidity of approximately 95%. Sufficient strength may be determined byrolling the granules between the thumb and finger after the notedexposure. If the granules have a solid feel similar to dry pellets, thenthe assumption is that they would have sufficient strength to surviveformulation processing, and they pass the storability test. But, if thepellets are mushy or soft and fall apart upon fingering, then they fail.

The strength of the granular substrate is determined through the crushstrength test, ASTM E 382 Volume 3.06, and resistance to attrition (RTA)test, ASTM E 728-91 Volume 11.04. The dispersible granular substrate ofthe present invention has a crush strength between 2 and 8 pounds on an8 mesh pellet. Additionally, in these embodiments, the granularsubstrate has an RTA value of at least 85%, more preferably at least90%.

The granular substrates of the invention generally have a smooth surfaceand are spherical in shape. The spherocity lends to desired flowcharacteristics of the substrates in bulk form. The angle of repose is atest utilized to measure the ability of a substrate to flow in bulkform. The test is conducted on a 14×30 mesh sample. The granularsubstrates of the invention preferably have an angle of repose of 35degrees or less.

The granular substrate should have the capability of absorbing theactive chemical agent in order to function as a carrier. The activeagent is generally absorbed in the carrier up to about five percent byweight. The substrate is also water soluble and therefore degrades uponexposure to moisture or water.

The dispersible granular substrate of the present invention is suitablefor use as a carrier for active chemical agents. For example, activechemical agents could include herbicides or other pesticides that arecommonly distributed through the use of a carrier in bulk form.

The following example, which constitutes the best mode presentlycontemplated by the inventors for practicing the present invention, ispresented solely for the purpose of further illustrating and disclosingthe present invention, and is not to be construed as a limitation on theinvention. All percentages used herein are weight percentages unlessspecifically stated otherwise.

EXAMPLE

The dry based materials, wood particle board flour and dolomiticlimestone powder, were thoroughly mixed in a ribbon type mixer beforeadding the binder composition. The binder composition, composed ofcalcium lignosulfonate in solution form, was added to the dry materialsand then mixed in a pin mixer or turbulator.

The resulting wet mixture was then fed into a rotating pelletizing pan.The substrates, in pellet form, were transported from the pelletizingpan to a vibrating fluid bed dryer where the granular substrates wereheated to remove excess water.

The finished granular substrates contained 1.2% wood particle boardflour, 7.6% calcium lignosulfonate solids, and 90.6% dolomitic limestonepowder, with 0.6% moisture being assumed. The granular substrates had anSGN of 140, a Uniformity Index (“UI”) of 40, a bulk density of 64 pcf,an RTA of 94%, pH of 7.9, and a dispersibility of less than 1 minute.

Due to the wood particle board flour in the composition, the finishedgranular substrate provides a kinetic energy release upon exposure tomoisture, as the swelling of the wood flour tears the granule apart. Thegranules of the invention also exhibit better storability thanconventional pelleted lime, and enhanced resistance to attrition andstorability.

In accordance with the provisions of the patent statutes, the presentinvention has been described in what is considered to represent itspreferred embodiment. However, it should be noted that the invention canbe practiced otherwise than as described without departing from itsspirit and scope.

1. An inert dispersible granular substrate suitable for use as a carrierfor chemical agents, comprising: (a) one or more mineral components, theone or more mineral components having a bulk density of greater thanabout 70 pounds per cubic foot; (b) one or more dispersibilityadditives; and (c) one or more water soluble binders; the granularsubstrate having a bulk density of from greater than 55 pounds pcf toabout 70 pcf, a water dispersibility of less than 5 minutes, a pH offrom 6 to 8, and sufficient strength to survive formulation processingafter 3 days of continuous exposure to a temperature of approximately75° F. and a relative humidity of approximately 95%.
 2. The inertdispersible granular substrate as recited in claim 1, wherein thegranular substrate has a bulk density of from about 57 pcf to about 67pcf.
 3. The inert dispersible granular substrate as recited in claim 1,wherein the granular substrate has a bulk density of from about 59 pcfto about 65 pcf.
 4. The inert dispersible granular substrate as recitedin claim 1, wherein said granular substrate has an RTA of at least 85%.5. The inert dispersible granular substrate as recited in claim 1,wherein said granular substrate has an RTA of at least 90%.
 6. The inertdispersible granular substrate as recited in claim 1, wherein said theone or more mineral components have a bulk density of from about 75 toabout 90 pounds per cubic foot.
 7. The inert dispersible granularsubstrate as recited in claim 1, wherein said granular substrate has awater dispersibility of less than 3 minutes.
 8. The inert dispersiblegranular substrate as recited in claim 1, wherein said granularsubstrate has a water dispersibility of less than 1 minute.
 9. The inertdispersible granular substrate as recited in claim 1, wherein saidgranular substrate has a particle size guide number of about 50 to about300 and a uniformity index of at least
 35. 10. The inert dispersiblegranular substrate as recited in claim 1, wherein said granularsubstrate has a particle size guide number of about 100 to about 230 anda uniformity index of at least
 40. 11. The inert dispersible granularsubstrate as recited in claim 1, wherein said granular substrate has atotal moisture content of 8% or less.
 12. The inert dispersible granularsubstrate as recited in claim 1, wherein said granular substrate has anangle of repose of 35 degrees or less.
 13. The inert dispersiblegranular substrate as recited in claim 1, wherein said dispersibilityadditive is one or more of the group consisting of expanded silica, flyash, hydrated lime, wood flour, wood particle board flour, distiller'sdried grain, thin stillage, ground wheat straw, cellulose, glycerins,glycols, cellulose, clay, soy flour, and mineral oil.
 14. The inertdispersible granular substrate as recited in claim 1, wherein saiddispersibility additive is wood flour containing an amount ofurea-formaldehyde resin.
 15. The inert dispersible granular substrate asrecited in claim 1, wherein said mineral component is one or more of thegroup consisting of dolomite and limestone.
 16. The inert dispersiblegranular substrate as recited in claim 1, wherein said mineral componentis dolomite.
 17. The inert dispersible granular substrate as recited inclaim 1, wherein said water soluble binder is one or more of the groupconsisting of brewers condensed solubles, fermentation solubles,lignosulfonate, sodium carbonate lignin, cane molasses, beet syrup, beetmolasses, desugared beet molasses, whey, starch, soy solubles with canemolasses or the like, hydrolyzed collagen, amino acid solutions, citrusresidium, cellulose derivatives, hemicellulose extract, urea liquor, orcellulose based polymer binders.
 18. The inert dispersible granularsubstrate as recited in claim 1, wherein the granular substrate has astrength such that, at a nominal particle size of 8 mesh, the granularsubstrate has a crush strength between 2 and 8 pounds.
 19. The inertdispersible granular substrate as recited in claim 1 having sufficientstrength to survive formulation processing after 4 days of continuousexposure to a temperature of approximately 75° F. and a relativehumidity of approximately 95%.
 20. The inert dispersible granularsubstrate as recited in claim 1 having a pH of from 6.5 to 7.5.
 21. Theinert dispersible granular substrate as recited in claim 1, wherein theone or more mineral components have a sizing of about 100% passingthrough a 30 mesh screen and about 50% or more passing through a 200mesh screen.
 22. A method of producing water dispersible granularsubstrates, comprising: (a) mixing one or more mineral components, theone or more mineral components having a bulk density greater than about70 pounds pcf, one or more dispersibility additives, and one or morewater soluble binders to form a granular substrate admixture; (b)pelletizing the admixture to form granular substrates; and (c) dryingthe granular substrates at a temperature sufficient to remove excessmoisture and produce finished granular substrates having a bulk densityof from greater than 55 pounds pcf to about 70 pcf and a waterdispersibility of less than 5 minutes.
 23. A method as recited in claim21, further comprising exposing the granular substrates to one or moreactive chemical agents such that the granular substrates absorb aneffective amount of the one or more active chemical agents.
 24. Agranular pesticide comprising: (a) a inert dispersible granularsubstrate comprised of: (i) one or more mineral components, the one ormore mineral components having a bulk density of greater than about 70pcf; (ii) one or more dispersibility additives; and (iii) one or morewater soluble binders; and (b) an active pesticide applied onto thedispersible granular substrate; the granular pesticide having a bulkdensity of from greater than 55 pcf to about 70 pcf and a waterdispersibility of less than 5 minutes.